1. Field of the Invention
The present invention relates to an operating method for a pump and a bearing device for a pump, and more particularly relates to a method of operating a vertical shaft pump used for drainage of rain water and a bearing device for the pump.
2. Description of the Related Art
A conventional technology in relation to a method of operating a pump and a bearing device for a pump according to the present invention will be described below with taking a ceramic bearing device for a vertical shaft pump used for drainage of rain water, referring to FIG. 13. FIG. 13 is a vertical cross-sectional view showing a conventional ceramic bearing device for a vertical shaft pump used for drainage of rain water. The reference character 1 indicates a pump main shaft, the reference character 3 indicates a ceramic bearing device, the reference character 9 indicates a casing flange portion, the reference character 10 indicates a pump casing and the reference character 32 indicates an impeller. In this example, three of the ceramic bearing devices 3 are mounted and fixed to the casing flange 9 or the pump casing 10. The impeller 32 rotates together with the pump main shaft 1, and the impeller 32 pumps the pumped water to flow up inside the pump casing 10.
The ceramic bearing is widely used for a bearing in a vertical shaft pump since it is generally superior in wear resistance and can use the pumped water as its lubricant.
In recent years, the amount of rain water flowing into a drainage pump station in a city is rapidly increasing because of rapid urbanization. In order to cope with this situation, there is a growing need for precursory standby operation of the drainage pump.
However, in the vertical shaft pump used for drainage of rain water often in such a precursory standby operation, the pump main shaft is rotated for a long period with on-load operation in which the water is not pumped. In such a case, since lubricating water is not injected into the bearing, occurrence of an abnormal wear in the bearing due to dry sliding cannot be avoided. That is, even if a ceramic bearing is employed, the occurrence of an abnormal wear in the bearing cannot be avoided.
A method solving such a problem is disclosed in Japanese Patent Application Laid-Open No. 2-115592 (1990), where lubricating water from a water source external to the drainage pump is injected into the bearing. In this method, by judging whether the bearing is immersed or not using a priming detector, the lubricating water is injected if the bearing is not immersed. And the lubricating water is stopped to be injected if the bearing is immersed.
A method coping with no-load operation for a short period using an oil retaining porous ceramic bearing is disclosed in Japanese Patent Application Laid-Open No. 59-155621 (1984) where the bearing sliding surface is lubricated with a small amount of oil exuded from the porous ceramic bearing with thermal expansion of the oil.
A method is also disclosed in Japanese Patent Application Laid-Open No. 55-90718 (1980) where no-load operation is performed by using clean water supplied from an external pump and stored in the inner peripheral portion of a protecting tube.
Further, a method is disclosed in Japanese Utility Model Application Laid-Open No. 4-36120 (1992) where a water tank is fixed to the pump main shaft and no-load operation is performed by lubricating the bearing using the water stored in the water tank.
However, in the lubricating construction of the ceramic bearing disclosed in Japanese Patent Application Laid-Open No. 2-115592 (1990), there is disadvantage in that a large amount of lubricating water is required when the no-load operation of the pump is performed for a long period since the water injected into the bearing is supplied from the external water source during the no-load operation. Further, since there is a water supplying piping system, the maintenance management for the piping system is required and, therefore, the labor for the maintenance will be increased.
In the oil retaining porous ceramic bearing disclosed in Japanese Patent Application Laid-Open No. 59-155621 (1984), lubrication is not sufficient and the temperature of the bearing increases since the amount of oil is small. Further, a shortage of oil will occurs since the small amount of the exuded oil does not return to the bearing. Therefore, it is impossible to repeat the on-load operation.
In the method where no-load operation is performed by using clean water supplied from an external pump and stored in the inner peripheral portion of a protecting tube as disclosed in Japanese Patent Application Laid-Open No. 55-90718 (1980), since there is a water supplying piping system, the maintenance management for the piping system is required and, therefore, the labor for the maintenance will be increased. This is similar to the case of Japanese Patent Application Laid-Open No. 2-115592 (1990).
In the lubricating method disclosed in Japanese Utility Model Application Laid-Open No. 4-36120 (1992), it is thought that when the pump starts to rotate, the water inside the water tank is moved toward the outer peripheral portion and splashed with the action of centrifugal force. Therefore, it is predicted that no-load operation for a long period will cause the shortage of the water inside the water tank to lose a stable lubrication characteristic of the bearing.
In other words, in the case of the lubricating construction of bearing, it is impossible to repeat the no-load operation for a long period without supply of lubricating water from the water source external to the pump.